Zhe Zhou

Modification and Potential Application of Short-Chain-Length Polyhydroxyalkanoate (SCL-PHA)

As the only kind of naturally-occurring biopolyester synthesized by various microorganisms, polyhydroxyalkanoate (PHA) shows a great market potential in packaging, fiber, biomedical, and other fields due to its biodegradablity, biocompatibility, and renewability. However, the inherent defects of scl-PHA with low 3HV or 4HB content, such as high stereoregularity, slow crystallization rate, and particularly the phenomena of formation of large-size spherulites and secondary crystallization, restrict the processing and stability of scl-PHA, as well as the application of its products. Many efforts have focused on the modification of scl-PHA to improve the mechanical properties and the applicability of obtained scl-PHA products. The modification of structure and property together with the potential applications of scl-PHA are covered in this review to give a comprehensive knowledge on the modification and processing of scl-PHA, including the effects of physical blending, chemical structure design, and processing conditions on the crystallization behaviors, thermal stability, and mechanical properties of scl-PHA.

Polypropylene Nanocomposites Based on Synthetic Organic-Soluble Ag Nanocrystals with Prominent β-nucleating Effect: Quiescent Crystallization and Melting Behavior

Differential scanning calorimetry, x-ray diffraction, and polarized optical microscopy were used to investigate the quiescent crystallization and melting behavior of isotactic polypropylene (iPP) nanocomposites based on synthetic organic-soluble Ag nanocrystals (NCs). The effects of Ag loading and crystallization temperature on the crystallization behavior and crystalline structure were studied. The results showed that the synthetic Ag NCs as a novel effective β-crystal nucleating agent for iPP could promote the overall crystallinity, decrease the size of spherulites, and induce the formation of large amounts of β-crystals in the nanocomposites under quiescent crystallization. The relative content of β-crystals significantly increased with increasing Ag loading, and slightly increased with decreasing crystallization temperature. The quiescent crystallization kinetics was analyzed using the Avrami model. The results showed that the iPP nanocomposites with added Ag NCs had higher crystallization rate constant (k) and lower crystallization half-times (t1/2) as well as the Avrami exponent (n) than pure iPP, indicating that the presence of Ag NCs acted as heterogeneous nucleating sites and promoted the crystallization rate of iPP.

Preparation and Characterization of TPU Toughened PLA Elastic Fibers

Poly (lactic acid) (PLA) elastic fibers were prepared by melt spinning using Thermoplastic polyurethane (TPU) as a toughing agent and PLA-g-MA(Maleic anhydride) as a compatibilizer. Thermal properties and thermal stability of PLA/TPU composites, as well as the cross section morphology and mechanical properties of fibers were studied in the present investigation. DSC results showed that PLA was immiscible with TPU. In addition, the incorporation of TPU decreased the melting enthalpy of PLA/TPU composites. TG results indicated that the initial degradation temperatures of composites were also decreased by the appearance of TPU, and it decreased by 9°Cwhen TPU content was up to 20wt%. FESEM results confirmed that strong interactions were existed between PLA and TPU phases, which were benefit for the improvement of PLA/TPU fibers’ mechanical properties. Results of tensile testing demonstrated that TPU could improve the toughness of fibers effectively and the elongation-at-break of fibers increased from 2.2% of PLA to 203.9% of PLA/TPU.

Synthesis, structure and thermal properties of poly(A-block-B-block-A) copolymer based on biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and amorphous polystyrene

Abstract A series of poly(A-block-B-block-A) copolymers based on biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and amorphous polystyrene (PS) were synthesised by atom transfer radical polymerisation (ATRP). The chemical structure, molecular weight and distribution were systematically characterised by Fourier transform infrared, 1H nuclear magnetic resonance (1H NMR) and gel permeation chromatography (GPC). The melting and crystallisation behaviours, and thermal stabilities of copolymers were investigated by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA); the degradation activation energy was calculated by Horowitz–Metzger method. Results showed that the maximum yield of triblock copolymer was 88%. DSC curves revealed that the triblock copolymers had their cold crystallisation temperature from 50·83 to 65·67°C, and the crystallinity from 55·60 to 12·60. TG curves showed that the thermal stabilities of triblock copolymers were enhanced, and its degradation activation energy decreased from 428 to 197 kJ mol−1.

Preparation of silver nanoparticles with hydrophobic surface and their polyester based nanocomposite fibres with excellent antibacterial properties

Abstract Silver nanoparticles with hydrophobic surface (HS-nano-Ag) of small size (<10 nm) and capped by 18 wt-% aliphatic acid were specially designed and prepared to improve their dispersibility in and phase compatibility with a polyester matrix. Polyester based nanocomposites with various HS-nano-Ag contents (0·1, 0·5, 1 and even 20 wt-%) were prepared by melt processing, and the effects of HS-nano-Ag additive on the structure and properties of polyester materials were investigated. The HS-nano-Ag had a fine and homogeneous dispersion in the polyester matrix as determined from transmission electron microscopy analysis. The polyester nanocomposites with lower content (≤500 ppm) of Ag had good spinnability, and the stress of the resulting fibres remained higher than 2·5 cN dtex−1 under non-optimised conditions. In addition, the resulting polyester fibres had good antibacterial rate (>96%) against Staphylococcus aureus and Escherichia coli when containing a low content of HS-nano-Ag (100 ppm).

The morphologies and fluorescence quantum yields of perylene diimide dye-doped PS and PHVB microspheres

Aggregation and continuous π-stacking have been the major obstacles hindering the fluorescence (FL) quantum yield (ΦF) of perylene diimide (PDI) derivatives in the condensed phase. To prepare polymer microspheres with nearly unity ΦF, in this work a POSS functionalized PDI derivative, POSS–PDI–POSS (PPP), was applied as the red fluorophore of poly(3-hydroxylbutyrate-co-3-hydroxyvalerate) (PHBV) and polystyrene (PS) microspheres. The electrosprayed PPP/PHBV and PPP/PS microspheres have unique hollow structures. Moreover, they show bright red FL under a fluorescence microscope. A photophysical study of the microspheres indicates a significant role of the polymer matrix in disrupting the aggregation state and the ΦF of the embedded PPP fluorophore. Both the PPP/PHBV and the PPP/PS microspheres show higher ΦF than most PDI materials in the condensed phase. The PPP/PHBV microspheres show ΦF of 28%, whereas the PPP/PS microspheres give nearly unity ΦF.

Melt-spun microbial poly(3-hydroxybutyrate-co-3-hydroxyvalerate) fibers with enhanced toughness: Synergistic effect of heterogeneous nucleation, long-chain branching and drawing process

A series of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) composite fibers were prepared via melt reactive processing where tungsten disulphide (WS2) and dicumyl peroxide (DCP) was used as heterogeneous nucleating agent and initiator, respectively. Compared with PHBV or PHBV/WS2 fiber, the resultant LCB-PHBV/WS2 fibers showed improving mechanical performance, a higher nucleation temperature and a rapid crystallization rate due to the synergistic effect between heterogeneous nucleation, long chain branched structure and draw-induced crystallization. Taking the results with a cooling rate of 20 °C/min as an example, the peak crystallization temperature of LCB-PHBV/1.0 wt%WS2 increased from 100.47 °C to 107.40 °C and the crystallization enthalpy increased from 87.95 J/g to 93.03 J/g. Moreover, two different crystalline forms, α-crystal and β-crystal, were found in the prepared PHBV fibers, and the β-crystal part increased with the inducement of the stretching ratio which enhanced the fiber strength, given the tensile strength and elongation at break of the LCB-PHBV/WS2 fibers up to 189.8 MPa and 46.5%, respectively.

The Synergistic Effect of Organic Phosphorous/α-Zirconium Phosphate on Flame-Retardant Poly(lactic acid) Fiber

The flame-retardant poly(lactic acid) (FR-PLA) fibers with different contents of modified α-zirconium phosphate (α-ZrP) and polysulfonyldiphenylene phenyl phosphonate (OP) were prepared by melt spinning. The organic modification of α-ZrP was characterized by Fourier transform infrared spectroscopy, wide angle X-ray diffraction, and thermo gravimetric analysis. The limiting oxygen index, vertical burning test, and cone calorimeter test were used to investigate the synergistic effect of OP/α-ZrP on flame-retardant property of FR-PLA, the test results suggested that the combustion of PLA fibers was efficiently inhibited by OP/α-ZrP. The results of scanning electron microscopy, Raman spectrum, and X-ray photoelectron spectroscopy indicated that the flame-retardant mechanism of OP/α-ZrP mainly depended on condensed phase. The tensile strength and morphology of FR-PLA fibers with OP/α-ZrP were better than those of fibers treated only with OP, demonstrating that α-ZrP could significantly improve the mechanical property of FR-PLA fibers.

Fully Biodegradable Films Based on Functionalized Natural Polyphenol/Poly(3-Hydroxybutyrate-co-3-Hydroxyvalerate) as a Potential Material for Food Packaging

As a potential material for food packaging, fully biodegradable composite films based on novel functionalized natural polyphenol/Poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) were successfully fabricated by solution casting, and also the functionalized natural polyphenol (C18TAx) was synthesized by grafting fatty acid onto natural polyphenol Tannic Acid (TA). The resultant C18TAx with better hydrophobicity was uniformly dispersed into a PHBV matrix. The influence of C18TAx dosage on the mechanical behavior, crystallization behavior and thermal properties of the C18TAx/PHBV composite films was investigated by uniaxial tensile mechanical testing, Differential Scanning Calorimeter (DSC), Polarizing Optical Microscope (POM) and Wide Angle X-ray Diffractometry (WAXD). The results revealed that the x value was about 0.09, showing that about 11/20 phenol hydroxy groups in TA molecules were replaced with fatty acid chains. Compared with those of neat PHBV, the tensile strength and elongation at break of the C18TA0.09/PHBV composite films with 10 wt.% C18TA0.09 content were enhanced by 121%, and 458%, respectively. This improvement was primarily ascribed to intermolecular hydrogen bonding interactions in composite films. This new type of fully biodegradable bio-based composite films shows great potential for food packaging.

Effects of Purification on the Structure and Properties of Hardwood Kraft Lignin

Poor melt spinnability of lignin hinders the development of lignin-based high-value products, which can attribute to the diversity of its component and structure. In this work, hardwood kraft lignin (HKL), which was obtained from paper pulping process, was filtered using a 0.05 μm ceramic membrane followed by the heat-treatment under vacuum to evaluate the effects of different purification on the chemical structure, components, and thermal properties of HKL. Results showed that the contents of ash and lignin-carbohydrate complexes (LCCs), the molecular weight and its distribution were significantly decreased after purification, while the basic structure of HKL did not change. The thermal stability and carbon content increased a lot after the heat-treatment, while the content of methoxy and β-β or β-1 linkages decreased. However, the melt spinnability of HKL decreased significantly and many defects appeared in the obtained carbon fibers after heat-treatment for a long time.